This invention relates to a semiconductor substrate and a process for producing the semiconductor substrate. More particularly, it relates to a semiconductor substrate having an insulating film of uniform film thickness on a substrate and having an excellent production reliability and to a process for producing the semiconductor substrate.
Various integrated circuits have been used in computers and various electronic devices and, with reduction in size and enhanced performance thereof, higher integration and higher performance of the circuits have been required as well as production reliability.
With respect to these integrated circuits, multi-layer wiring circuits as shown in FIG. 8 have conventionally been used for raising the degree of integration of semiconductor integrated circuits.
Referring to the steps for producing semiconductor substrates of the integrated circuits, an oxide film is formed as a first insulating film 32 on a substrate 31 such as silicon, then a first wiring layer 33 composed of an aluminum film or the like is formed on the first insulating film surface. Subsequently, an inter layer dielectric film 34 such as a silica film or a silicon nitride film is deposited thereon by CVD method or plasma CVD method; a silica insulating film (planalizing film) 35 for planalizing the inter layer dielectric film 34 is formed on the inter layer dielectric film; a second insulating film 36 is deposited, if necessary, on the silica insulating film 35; a second wiring layer (not shown) is formed; and, if necessary, an inter layer dielectric film, a planalizing film, and an insulating film are further formed on the second wiring layer, the resulting product being used as a highly integrated circuits having the multi-layer wiring structure.
Also, a semiconductor substrate as illustrated in FIG. 9 is known.
On a substrate 31 are formed an oxide film as a first insulating film 32, an inter layer dielectric film 34 (if necessary), and an insulating film 35 in this order, and a circuit 33 is formed in this layered film (insulating film) and, further, a second insulating film 36 is formed on the insulating film 35 and the circuit. This constitution is referred to as a first wiring layer.
Further, a second wiring layer (not shown) having the same structure as that of the first wiring layer is formed on the second insulating film 36. The first wiring layer and the second wiring layer are connected to each other through a through-hole which is a connecting groove (not shown). In the same manner, a third wiring layer or more of the wiring layers may be formed thereon.
The inter layer dielectric film having the multi-layer wiring structure is provided for the purpose of planalizing an uneven surface of a substrate or a wiring layer as well as for ensuring insulation between an upper layer and a lower layer (between a substrate and a wiring layer thereon, or between an upper wiring layer and a lower wiring layer).
As a method for forming such inter layer dielectric film, there are illustrated: (1) a method of forming a SiO2 film on the surface of a substrate by a chemical vapor deposition (CVD) of a compound gas such as SiH4; (2) a method of forming a SiO2 film on the surface of a substrate by plasma deposition of tetraethoxysilane (TEOS); and (3) a method of forming a SiO2 film by coating a siloxane-based coating liquid or a silazane-based coating liquid to the surface of a substrate by a spin coating.
Of these methods, the above method (3) using a spin coater is preferred for forming the inter layer dielectric film because of its large throughput capacity and for forming a smooth film whose surface was planalized. However, there have been cases where a projected portion is formed as a protuberance of the coating film as shown in FIG. 1 after spin coating the coating liquid because the coating liquid is centrifuged to the periphery of a silicon wafer as a substrate. FIG. 1 shows a schematic cross section of the projected portion formed at the edge of the periphery.
Such periphery of the silicon wafer might contact with other constituent member and be stained therewith and, during conveying the wafer, the projected portion of the insulating film at the periphery edge thereof might contact with other devices thereby to develop some cracks. Development of such cracks means generation of a large number of unwanted foreign matter, which might lead to a serious reduction in production yield.
Therefore, for example, Japanese Patent Laid-Open No. 316186/1996 proposes to wash away the projected portion by ejecting a solvent, usually downward to the projected portion after spin-coating, for the purpose of removing the projected portion at the periphery of the silicon wafer.
In this case, however, a bump is formed in some cases as shown in FIG. 10A, though depending upon the kind of the coating liquid (e.g., types of the insulating component and the solvent, and its contents) or a solvent to be used for washing. Such bump may invite the collection of foreign matter as in the case of a projected portion. Further, in a situation where a coating film is formed on the first insulating film such as in forming the inter layer dielectric film, a condition results as shown in FIG. 10B which involves the problem that, when the surface is mechanically polished as needed, the underlying first insulating layer (coating film) becomes bare as shown in FIG. 10C, thus the resulting semiconductor substrate becomes inferior in chemical resistance.
The present invention intends to solve the above-described problems with the prior art and to provide a process for producing, with a high yield and an excellent production reliability, a semiconductor substrate having no projected portion or protuberance and no bump, and therefore suffering no cracking and generating no foreign matter and having an excellent chemical resistance.
The process of the present invention for producing semiconductor substrates is characterized by comprising the steps of:
(a) forming a coating film by coating an insulating film-forming coating liquid on a substrate mounted on a rotating disc of a spin coater according to a spin coating method; and then
(b) removing a projected portion of the coating film formed at the periphery of the substrate by ejecting a solvent through a nozzle moving from any point on a line drawn between the periphery edge and the center of the substrate toward the periphery edge while rotating the substrate.
The coating liquid for forming the insulating film (SOG film) preferably comprises one or more of silicon-containing compound selected from the group consisting of an alkoxysilane represented by the following general formula (I) or its hydrolyzate and a halogenated silane represented by the following general formula (II) or its hydrolyzate, and an organic solvent:
XnSi(OR)4-nxe2x80x83xe2x80x83(I) 
XnSiXxe2x80x24-nxe2x80x83xe2x80x83(II) 
wherein X represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 8 carbon atoms, a fluorine-substituted alkyl group, an aryl group or a vinyl group, R represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group, Xxe2x80x2 represents a halogen atom, and n represents an integer of 0 to 3, provided that when silicon compounds represented by the above general formulae (I) and (II) are used together, at least one of X in the above general formulae (I) and (II) represents H (hydrogen atom).
The coating liquid for forming the insulating film (SOG film) preferably comprises one or more of silicon-containing compound selected from the group consisting of a polysilazane having a repeating unit represented by the following general formula (III), and an organic solvent: 
wherein R1, R2 and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.
The coating liquid for forming the insulating film (SOG film) preferably comprises one or more of silicon-containing compound selected from the group consisting of an alkoxysilane represented by the following general formula (I) or its hydrolyzate and a halogenated silane represented by the following general formula (II) or its hydrolyzate, one or more of silicon-containing compound selected from the group consisting of a polysilazane having a repeating unit represented by the following general formula (III), and an organic solvent:
XnSi(OR)4-nxe2x80x83xe2x80x83(I) 
XnSiXxe2x80x24-nxe2x80x83xe2x80x83(II) 
wherein X represents a hydrogen atom, a fluorine atom, an alkyl group having 1 to 8 carbon atoms, a fluorine-substituted alkyl group, an aryl group or a vinyl group, R represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an aryl group or a vinyl group, Xxe2x80x2 represents a halogen atom, and n represents an integer of 0 to 3, provided that when silicon compounds represented by the above general formulae (I) and (II) are used together, at least one of X in the above general formulae (I) and (II) represents H (hydrogen atom); 
wherein R1, R2 and R3 each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.
It is preferred that the coating liquid for forming the insulating film (SOG film) further contains an easily decomposable resin.
The semiconductor substrate of the present invention is a semiconductor substrate obtained by the above-described process, wherein the insulating film on the substrate has an average film thickness (T) of from 0.1 to 6 xcexcm, and the relation between thickness of the insulating film at the periphery (TE) and the average film thickness (T) is represented by the following formula:
0.8T less than TE less than 1.2T. 